Omega-3 Improves Your Pet Health

vet shaved off all hair. could this cause a health problem?

She is 20 years old, spayed female. Never any health problems but she has lost weight due to natural aging processes. I know she’s sliding downhill.
Lately she has begun yowling very loudly. She does it most of the time in the kitchen, staring in a corner. The only way to stop her is to tap her on the head and she just stops and turns to look at me as if to say “oh….sorry.” We recently had to put one of her kitty buddies to sleep as he had cancer. Can she be missing him?
Also, she is a longhaired cat and tends to have a very matted coat as she detests brushing and will do damage to me if I try to brush her. I try to untangle it and cut the matted stuff off but there are still a few bad ones that I just can’t make a dent in. I’m also afraid that if I try to brush her or get too close to her skin, I will cut her and she has very thin skin. I have a mat brush which helps somewhat but I don’t want to hurt her. Any suggestions as how to keep her relativel mat-free?